1. Technical Field
The invention relates to a rotary pump having an adjustable, preferably variable, delivery volume, and a method for manufacturing it. The rotary pump can in particular be used as a lube oil pump for supplying lube oil to an internal combustion engine, in particular an internal combustion engine of a motor vehicle engine.
2. Description of the Related Art
Lube oil pumps in motor vehicles are driven in accordance with the rotational speed of the engine which is to be supplied with the lube oil, usually directly or via a mechanical gearing of the engine. The rotational speed of the pump correspondingly increases with the rotational speed of the engine. Since rotary pumps have a constant specific delivery volume, i.e. they deliver substantially the same amount of fluid per revolution at any rotational speed, the delivery volume increases in proportion to the rotational speed of the pump. The engine's requirement also increases roughly in proportion to the rotational speed of the engine, up to a certain limiting rotational speed, beyond which however it deviates or at least levels out, such that when the limiting rotational speed is exceeded, the rotary pump delivers beyond the requirement. Adjustable rotary pumps have been developed in order to not have to direct the excess delivered amount into a reservoir, which incurs losses. Examples of adjustable rotary pumps include the internal-axle and external-axle toothed wheel pumps known from DE 102 22 131 B4. Adjustable vane pumps are also known. These pumps each comprise an actuating member which can be moved back and forth. In the examples cited, the delivery rotor is either a toothed wheel or a vane. In the known internal-axle toothed wheel pumps and vane pumps, the movement of the adjusting member adjusts the eccentricity between two mutually mating toothed wheels or the eccentricity between the vane and the actuating member in accordance with the requirement of the consumer. In external-axle toothed wheel pumps, the axial engagement length of two toothed wheels is adjusted. For adjusting, the respective actuating member is charged with an actuating force, for example charged directly with the high-pressure fluid.
The actuating force is counteracted by a spring member. In pumps of the type cited, which are increasingly manufactured from light metal alloys, in particular aluminum alloys, the surfaces of the pump casing and of the actuating member which are in frictional contact are surprisingly subject to particular wear and determine the service life of the pump.